Intersubband all-optical switching based on Coulomb-induced optical nonlinearities in GaN/AlGaN coupled quantum wells

Intersubband ( ISB) transitions in wide-conduction-band-offset GaN/AlGaN quantum wells are promising for all-optical switching applications in fibre-optic networking, due to their ultrafast relaxation times and great design flexibility. Here we describe a novel approach to cross-absorption modulation with these materials, in which optical control pulses are used to produce a large Stark shift of the intersubband absorption spectrum through a redistribution of electrons in coupled quantum wells. This mechanism is strongly enhanced by the intrinsic polarization fields of nitride heterostructures. A numerical model based on the self-consistent time-domain solution of the Schrodinger, Poisson and carrier-density rate equations has been developed to design coupled quantum wells optimized for this application. Simulations indicate that in these structures the saturation intensity is over 30 times smaller compared to the case of cross-absorption modulation in uncoupled GaN/AlGaN quantum wells.